The amplitude of the light-evoked inward current recorded from depolarizing retinal bipolar cells may be more than doubled by a mixture of 20 microM CNQX and AP-7. These glutamate antagonists also induce a steady outward current, reduce the baseline noise, and decrease the amplitude of the rod-driven inward current that persists after the end of a bright stimulus. Because the latter observations indicate that the effect of CNQX and AP-7 is more complex than simply suppression of the chloride-dependent input, the increase in amplitude of the light-evoked inward current cannot be used to estimate the intracellular chloride concentration.